Recent reports by the World Climate Research Programme and the National Research Council, including “Adequacy of Climate Observing Systems” (1999), have noted that current observational networks are inadequate for monitoring the Earth's climate system. The accuracy and fidelity of the data used to measure climate variability are crucial to both U.S. government monitoring efforts and U.S. industry. Even small biases can alter the interpretation of decadal climate variability and change. Although the United States is a leader in climate research, no national observing network is capable of ensuring long-term climate records free of artificial biases—also known as inhomogeneitie—due to factors such as instrument changes, station relocations, and changes in the surrounding environment.